Such a locking device is known from DE 10242825 A1. With regard to the prior art, further reference is also made to DE 197 09 149 A1 and DE 27 29 770 C2. Such locking devices are also referred to as multi-pin locking devices. They make a secure latching and a fine-stepped longitudinal adjustment possible. In the blocked position, two blocking pins rest against one latching web adjacent to them, respectively. With their tapering region, the blocking pins rests against the latching web. The tapering region is formed as a frusto-conical region; it is situated between the front region and the shaft region of the blocking pins. A blocking pin blocks in only one displacement direction, respectively. The two blocking pins block in different displacement directions. The angle at which the tapering region rests against the latching web lies in the range of a self-locking action.
Since only one blocking pin is generally responsible for locking a displacement direction, during an exposure to a load, the entire locking forces act upon this one blocking pin and the corresponding latching web against which the blocking pin rests. Due to the load, the blocking pin positions itself slightly obliquely within its guide in the blocking unit, which leads to an increase of the angle at which the tapering region rests against the latching web. In the case of a repeated load, i.e. when driving over several road bumps or in case of pressure on a backrest of the motor vehicle seat, the blocking pin responsible for locking is more or less pushed out, i.e. pushed upwards in the z direction, from the latching opening which it has engaged. This is a disadvantage. Though this pushing-out does not lead to a complete release of the lock because at least one further blocking pin is in engagement with a latching opening and because other blocking pins can latch in subsequently, it does lead to a certain readjustment of the vehicle seat in the longitudinal direction. This effect can repeat itself several times.
It is disadvantageous if a blocking pin is pushed out of the locking mechanism. The forces that put an upwardly directed load on the blocking pin should be as small as possible. It has to be prevented that the blocking pin is released from the associated latching web.